How in the sweet hell does a team with "D" rated defense and "C+" rated offense have "B-" rated coaching?

Probably because the personnel the coach had to work with is either too young and inexperienced(ie, mistake prone), or declining and ineffective. It was an identical roster to the one that finished second worst in the league last year, with the only changes made of the type that typically don't greatly improve a team(bottom 6 defenseman, 2 rookies).

The areas you'd really expect coaching and tactics to play a major role have all been very good otherwise(Special teams).